Could you supply a link to that letter?
My research shows St. John of Damascene in the 8th Century was the 1st to propose that
Sorry, I can't. You could contact the Web site's editor.
'The tone of authority with which the letter speaks is noteworthy, especially in the later part (56, 58, etc.): "But if certain persons should be disobedient unto the words spoken by Him through us let them understand that they will entangle themselves in no slight transgression and danger; but we shall be guiltless of this sin" (59). "It may, perhaps, seem strange", writes [distinguished Anglican scholar] Bishop [J.B.] Lightfoot, "to describe this noble remonstrance as the first step towards papal domination. And yet undoubtedly this is the case." (I, 70.)' - http://www.newadvent.org/cathen/04012c.htm